Pulpwood grinder control



April 18, 1967 H|LL 3,314,615

PULPWOOD GRINDER CONTROL Filed April 21, 1964 5 Sheets-Sheet l INVENTOR.JQHN L. HlLL April 18, 1967 J. L. HILL 3,314,615

PULPWOOD GRINDER CONTROL Filed April 21, 1964 3 Sheets-Sheet 2 as I 36FIG. 2

INVENTOR. JOHN L. Hl ILL April 18, 1967 J. L. HILL 3,314,615

PULPWOOD GRINDER CONTROL Filed April 21, 1964 3 Sheets-Sheet 5 INVENTOR.JOHN L. H ILL United States Patent 3,314,615 PULPWOOD GRINDER CONTROLJohn L. Hill, Fort Frances, Ontario, Canada, assignor to Boise CascadeCorporation, Boise, Idaho, at corporation of Delaware.

Filed Apr. 21, 1964, Ser. No. 361,344 3 Claims. (Cl. 241--34) Thisinvention relates generally to pulpwood grinding apparatus, and moreparticularly to grinding apparatus including control means for effectinga substantially constant rate of pulpwood feed relative to the grindingstone surface.

Mechanical or groundwood pulp is produced by pressing a peeled or barkedpulpwood log against the surface of a revolving stone, the rotating axisof the stone being substantially parallel with the fiber direction ofthe log. The .usual arrangement of pulp grinding devices involves asynchronous grinding motor carrying a pair of grinding wheels at eitherend, and mounted in pockets, each grinding wheel or stone having amagazine on at least either side adapted to receive logs. A pressurecylinder is mounted in conjunction with each magazine having a pressurefoot which is activated thereby and forces the logs against the grindingwheel. The system employed for actuating the hydraulic pressurecylinders in the conventional arrangement includes a reservoir of waterand a pump which provides pressure water from the reservoir, whichpasses through a governor.

The principal variables in mechanical pulping are stone surface, stonespeed, grinding pressure, power input, energy consumption, production,temperature of grinding, consistency of grinding, freeness and strengthof pulp, and Wood variables. There is a definite relationship betweenpulp properties, such as freeness and strength and grindingcharacteristics such as energy consumption and production.

Modern practice in groundwood operation is to operate at increasinglyhigher surface speeds, higher pressures, and with longer wood. Theprincipal types of grinders may be considered pocket, chain and ring.With any of these types of grinders a great deal of difliculty has beenexperienced in maintaining proper and substantially uni form freeness.This in part is due to maintaining a con stant load on the drive motor.This method of control is insensitive to the grinding rate.

An object of this invention is to provide a substantially constant andcontrollable grinding rate per square inch of wood in contact with thegrinding surface.

A further object of the invention is to provide a control unit comprisedof a plurality of interoperatively'related valve means designed tocontrol one pressure cylinder and employing low pressure fluid forinitial control of the pressure foot piston of the pressure cylinderwhich the control unit serves in its advancing and retiring movement.

A still further object of the invention is to provide a control unit asbefore which includes means whereby high-pressure fluid may be appliedto drive the pressure foot under load.

With these and other objects in view the invention generally relates toa method and apparatus for controlling power applied to the means forforcing pulpwood against a motor driven grindstone.

FIGURE 1 is a diagrammatic view of a control unit in relation to agrinding unit;

FIGURE 2 is a sectional side elevation view of a pocket grinder;

FIGURE 3 is an enlarged side elevational view of a control unit; and

FIGURE 4 is an enlarged section view of control unit shaft.

Referring to the drawings in detail indicates a grind- 3,314,615Patented Apr. 18, 1967 stone driven by a suitable means (not shown).Pulpwood 12 is forced against the revolving surface of the grind stoneby pressure foot 14 which is attached to piston rod 20 of cylinder 22 inwhich is movable mounted piston 24. Extending from the pressure foot isan extension member 16 to which is attached a cable or line 48. Thepressure foot 14 is caused to retract by forcing low pressure fluid suchas water to the left hand side of cylinder 22 via conduit 31, valve 30and conduit 26, the fluid in the right hand side of the cylinder beingreturned to sump via conduit 36, proportioning valve 38, valve 42 andconduits 44 and 43. During this retraction of the piston, valves 28, 32and 40 are closed. After the pulpwood 12 is inserted in the pocket,valves 30 and 42 are closed and valve 28 is opened, whereupon lowpressure fluid is supplied to the right hand side of the cylinder viaconduit 31, valves 32, 40 and 38, and conduit 36, the left hand side ofthe cylinder being connected with sump via conduit 26, valve 28 andconduits 46 and 43. During the initial movement of the pressure foot inthe forward direction low pressure fluid (for example water at p.s.i.)is admitted through valves 32, 4t) and 38 to the cylinder 22. The fluidflow is controlled by valve 38 which in turn is controlled by pressuretransmitted controller 35 which senses the fluid pressure in thecylinder 22, and as the pressure builds up cuts the flow of fluid supplyby activating proportioning valve 38. When an adjustable predeterminedpressure is obtained controller 35 causes valve 38 to close and holdsvalve 38 closed until the pressure in the cylinder drops to anadjustable and predetermined value. On closure of valve 33 valve 78opens admitting high pressure fluid (for example water under 400 p.s.i.)from conduit 76 as controlled by the opening of valve 74 which isoperable by grinder control mech-' anism hereinafter to be described.

It is to be understood that the controls for rate oof pulpwood feed tothe grinder stone surface may take various forms. The rate of pulpwoodfeed to the stone surface is selected and maintained by comparing therate of ram movement with a reference speed standard, in the drawing asynchronous motor.

The reference speed standard may take many forms other. than thatdisclosed in the drawings. As an example a suitably designed,alternating or direct current motor supplied from a constant potentialsource could be used. If such a motor was connected to a constantpotential source .through a voltage divider potentiometer then a rangeof reference speeds could be obtained. This arrangement would take theplace of the stepped cone pulley.

Instead of measuring the ram rate of travel directly as shown in thedrawings the measure of the water flow rate into cylinder 22 could beemployed as a measure of the ram speed. If the rate of flow intocyllinder 22 was employed a flow meter would be incorporated in thesystem between the cylinder 22 and the high pressure supply. Where aflow meter was employed the rate of flow signal from the flow meterwould activate a pneumatic controller. Such controller would control aproportioning valve in the high pressure water supply conduit to thecylinder 22. Employing this arrangement whenever the flow deviated fromthe controller set point the controller would activate the proportioningvalve to restore flow rate to the proper value. The activating of thepneumatic controller can be accomplished by the use of a signal from anelectrical generator driven from the ram 14.

From the foregoing it can be seen that the basis sensing device for thegrinder control must sense either (1) rate of mechanical motion, (2)fluid displacement, or (3) pulp stock characteristics.

A synchronous motor 58 has its shaft 52 pivoted on bearings 54 and 56.Mounted on motor shaft extension is stepped cone pulley 50. Attached tomotor 58 is frame member 68 which is connected to a suitable controller62 by means of rod or linkage 66. The controller 62 activates valve 74to proportionally control the fluid fiow to ram cylinder 22 and thusmaintain a substantially constant ram speed. A cable 48 is attached tothe ram 14 and is passed over the stepped pulley 58, the free end of thecable 18 being secured to a weight 60.

In FIGURE 3 is shown an enlarged view of the synchronous motor 58 andcontroller 62. The motor 58 is restrained by members 82 and 84 wherebythe motor housing can move. The movement of motor housing is controlledby stops 86 and 90 that are mounted in supports 82 and 84 and aresecured in the desired position by nuts 88 and 92.

In FIGURE 4 is shown an enlarged sectional view of the motor and pulleyshaft. The motor 58 has a shaft 52 coupled with an intermediate shaft 51by coupling means 94. Shaft 51 is supported by bearings 95, the pulley50 being rotatably mounted on the shaft. A slip clutch 96 serves totransmit torque between the pulley and the shaft 51. One purpose of theclutch is to permit normal torque to be transmitted and still allows themembers to slip in relation to each other during the period when the ramis retracting and/ or filling under low pressure fluid supply. Thetension on spring 98 is adjustable and maintained in the predeterminedposition by lock nuts 100. The number of grooves on the pulley may vary,and the larger the number of grooves, the greater is the range of ramspeed that may be controlled.

The speed of travel of the ram 14 is transmitted through cable 48 whichdrives the stepped cone pulley 50 at the same rotational speed as theshaft of motor 58. The motor frame will be in motion when there is adifference in speed of rotation between the motor shaft and the conepulley. The differential effect causes the synchronous motor frame tomove within the limits defined by stops 86 and 90. The movement of themotor frame is proportional to the angular difference between thesynchronous motor shaft speed and the speed imposed by therotationalspeed of the cone pulley. The motor frame through linkage 68, 66, and 64transmits its movement to controller 62 which activates valve 74 toproportionally control the flow of fluid to the ram cylinder 22 and thusmaintains constant ram speed.

The important step of the process is to control the "grinding rate perunit of wood in contact with the grinding surface. Controlling the rateof feed to the stone surface reduces up to 50% in freeness variations.At the same time the pulp strength is increased about and the finescreen rejects are lowered as much as 10%.

What is claimed is:

1. In a wood grinding apparatus including a rotating grinding stone anda pocket for receiving the wood to be ground, the invention whichcomprises a pressure foot for pressing the wood into contact with thegrinding stone;

4, piston and cylinder motor means for actuating said pressure foot; alow pressure fluid source; a high pressure fluid source; alternatelyoperable first and second means for connecting said low pressure andhigh pressure fluid sources, respectively, with said motor means toactuate said pressure foot in the wood pressing direction, said secondmeans including a control valve; controller means for operating saidcontrol valve to establish a predetermined rate of movement of saidpressure foot in the wood pressing direction; and controller operatingmeans responsive to a deviation in the rate of movement of said pressurefoot from said predetermined value for operating said controller meansand said control valve to return the rate of movement of said pressurefoot to said predetermined value. 2. In a wood grinder having arotatable grinding stone, a pocket to receive wood to be ground, apressure foot for pressing said wood into contact with said grindingstone, and a fluid actuated power unit for actuating said pressure foot,the invention which comprises a first source of fluid under pressureconnected to said power unit, a second source of fluid under higherpressure connected to said power unit, a valve for controlling thesupply of fluid under pressure from said second source to said powerunit, and means for advancing said pressure foot at a constant rateduring grinding, comprising a stepped cone pulley, means for operativelyconnecting the said pulley to said pressure foot, a synchronous motorconnected to said stepped cone pulley, and means connecting said motorto said valve.

3. In a wood grinder having a rotatable grinding stone, a pocket toreceive wood to be ground, a pressure foot for-pressing wood intogrinding contact with said grinding stone, and a double acting hydrauliccylinder and piston power unit for activating said pressure foot, theinvention which comprises a first source of fluid under pressureconnected to said cylinder, a second source of fluid under higherpressure than said first source connected to said cylinder, a valve forcontrolling the supply of fluid from said second source to saidcylinder, a synchronous motor operatively connected to said valve, astepped cone pulley connected to said motor, and a cable attached tosaid pressure foot and passing over said stepped pulley.

References Cited by the Examiner UNITED STATES PATENTS 1,766,548 6/1930Schnitzer 241-34 X 2,545,260 3/1951 Cole 241-34 X 2,965,315 12/1960Lyall 241--34 WILLIAM W. DYER, 1a., Primary Examiner.

H. F. PEPPER, Assistant Examiner.

1. IN A WOOD GRINDING APPARATUS INCLUDING A ROTATING GRINDING STONE ANDA POCKET FOR RECEIVING THE WOOD TO BE GROUND, THE INVENTION WHICHCOMPRISES A PRESSURE FOOT FOR PRESSING THE WOOD INTO CONTACT WITH THEGRINDING STONE; PISTON AND CYLINDER MOTOR MEANS FOR ACTUATING SAIDPRESSURE FOOT; A LOW PRESSURE FLUID SOURCE; A HIGH PRESSURE FLUIDSOURCE; ALTERNATELY OPERABLE FIRST AND SECOND MEANS FOR CONNECTING SAIDLOW PRESSURE AND HIGH PRESSURE FLUID SOURCES, RESPECTIVELY, WITH SAIDMOTOR MEANS TO ACTUATE SAID PRESSURE FOOT IN THE WOOD PRESSINGDIRECTION, SAID SECOND MEANS INCLUDING A CONTROL VALVE; CONTROLLER MEANSFOR OPERATING SAID CONTROL VALVE TO ESTABLISH A PREDETERMINED RATE OFMOVEMENT OF SAID PRESSURE FOOT IN THE WOOD PRESSING DIRECTION; ANDCONTROLLER OPERATING MEANS RESPONSIVE TO A DEVIATION IN THE RATE OFMOVEMENT OF SAID PRESSURE FOOT FROM SAID PREDETERMINED VALUE FOROPERATING SAID CONTROLLER MEANS AND SAID CONTROL VALVE TO RETURN THERATE OF MOVEMENT OF SAID PRESSURE FOOT TO SAID PREDETERMINED VALUE.